diff --git a/packages/protocol/contracts/governance/DowntimeSlasher.sol b/packages/protocol/contracts/governance/DowntimeSlasher.sol
index ed37cee69f9..ce2ea171dcd 100644
--- a/packages/protocol/contracts/governance/DowntimeSlasher.sol
+++ b/packages/protocol/contracts/governance/DowntimeSlasher.sol
@@ -83,7 +83,9 @@ contract DowntimeSlasher is SlasherUtil {
       uint256 signerIndex = epochNumberOfBlock(n, sz) == startEpoch
         ? startSignerIndex
         : endSignerIndex;
-      if (uint256(getParentSealBitmap(n)) & (1 << signerIndex) != 0) return false;
+      // We want to check signers for block n,
+      // so we get the parent seal bitmap for the next block
+      if (uint256(getParentSealBitmap(n + 1)) & (1 << signerIndex) != 0) return false;
     }
     return true;
   }
diff --git a/packages/protocol/test/governance/downtime_slasher.ts b/packages/protocol/test/governance/downtime_slasher.ts
index d5c3128356a..2bf440c63f0 100644
--- a/packages/protocol/test/governance/downtime_slasher.ts
+++ b/packages/protocol/test/governance/downtime_slasher.ts
@@ -1,5 +1,5 @@
 import { CeloContractName } from '@celo/protocol/lib/registry-utils'
-import { assertContainSubset, assertRevert } from '@celo/protocol/lib/test-utils'
+import { assertContainSubset, assertRevert, jsonRpc } from '@celo/protocol/lib/test-utils'
 import BigNumber from 'bignumber.js'
 import {
   AccountsContract,
@@ -37,7 +37,7 @@ contract('DowntimeSlasher', (accounts: string[]) => {
 
   const slashingPenalty = 10000
   const slashingReward = 100
-  const slashableDowntime = 3
+  const slashableDowntime = 10
 
   beforeEach(async () => {
     accountsInstance = await Accounts.new()
@@ -70,7 +70,7 @@ contract('DowntimeSlasher', (accounts: string[]) => {
     })
     it('should have set slashable downtime', async () => {
       const res = await slasher.slashableDowntime()
-      assert.equal(res.toNumber(), 3)
+      assert.equal(res.toNumber(), slashableDowntime)
     })
     it('can only be called once', async () => {
       await assertRevert(slasher.initialize(registry.address, 10000, 100, 2))
@@ -132,28 +132,54 @@ contract('DowntimeSlasher', (accounts: string[]) => {
   describe('#slash()', () => {
     let blockNumber: number
     let startBlock: number
+    let changeBlock: number
     const validatorIndex = 0
+    before(async () => {
+      let bn: number = 0
+      do {
+        bn = await web3.eth.getBlockNumber()
+        await jsonRpc(web3, 'evm_mine', [])
+      } while (bn < 350)
+    })
     beforeEach(async () => {
       blockNumber = await web3.eth.getBlockNumber()
       startBlock = blockNumber - 50
       const epoch = (await slasher.getEpochNumberOfBlock(blockNumber)).toNumber()
       await slasher.setEpochSigner(epoch, validatorIndex, validator)
       await slasher.setEpochSigner(epoch - 1, validatorIndex, validator)
+      await slasher.setEpochSigner(epoch - 2, 1, validator)
       await slasher.setEpochSigner(epoch + 1, validatorIndex, validator)
       // Signed by validators 0 and 1
       const bitmap = '0x0000000000000000000000000000000000000000000000000000000000000003'
       // Signed by validator 1
       const bitmap2 = '0x0000000000000000000000000000000000000000000000000000000000000002'
+      // Signed by validator 0
+      const bitmap3 = '0x0000000000000000000000000000000000000000000000000000000000000001'
       await slasher.setParentSealBitmap(blockNumber, bitmap)
       await slasher.setParentSealBitmap(blockNumber + 1, bitmap)
       await slasher.setParentSealBitmap(blockNumber + 2, bitmap2)
       await slasher.setNumberValidators(2)
+      // when epoch-2 changes to epoch-1, the validator to be slashed is down, but our signer number changes
+      // another validator is up around the epoch change
+      changeBlock = (epoch - 1) * 100 - 3
+      async function prepareBlock(bn) {
+        const parentEpoch = (await slasher.getEpochNumberOfBlock(bn - 1)).toNumber()
+        await slasher.setParentSealBitmap(bn, parentEpoch === epoch - 2 ? bitmap3 : bitmap2)
+      }
+      for (let i = 0; i < 7; i++) {
+        await prepareBlock(changeBlock + i)
+      }
     })
     it('fails if they were signed', async () => {
       await assertRevert(
         slasher.slash(blockNumber, validatorIndex, validatorIndex, 0, [], [], [], [], [], [])
       )
     })
+    it('success with validator index change', async () => {
+      await slasher.slash(changeBlock, 1, validatorIndex, 0, [], [], [], [], [], [])
+      const balance = await mockLockedGold.accountTotalLockedGold(validator)
+      assert.equal(balance.toNumber(), 40000)
+    })
     it('decrements gold when success', async () => {
       await slasher.slash(startBlock, validatorIndex, validatorIndex, 0, [], [], [], [], [], [])
       const balance = await mockLockedGold.accountTotalLockedGold(validator)